1. Field of the Invention
The present invention generally relates to a rate control method, and more particularly to a rate control method of perceptual-based rate-distortion (R-D) optimized bit allocation.
2. Description of Related Art
The goal of rate control in video coding is to regulate encoded bit stream without violating the constraints imposed by the encoder/decoder buffer size and the available channel bandwidth. The rate-distortion optimization (RDO) framework is employed in an H.264 coder to achieve a better tradeoff between rate and distortion. However, the RDO framework makes the rate control for H.264 more complicated. The reason is that the RDO process cannot proceed without quantization parameter (QP) being determined beforehand; on the other hand, some models such as rate-distortion (R-D) model and distortion-quantization (D-Q) model used to determine QP require the statistics generated from the RDO (a well-known chicken-and-egg dilemma).
Bit allocation and control methods have been conventionally proposed, some of which include R-D optimization but use distortion metrics such as mean square error (MSE) that are poorly correlated with perceptual quality because they do not take the characteristics of human visual system into consideration; while the others of which use perceptual-based metrics but do not take account of the R-D optimization.
Since the ultimate receivers of encoded video are human eyes, a need has arisen to propose a rate control method of both perceptual-based and rate-distortion (R-D) optimization to improve video quality.